510 REPORT— 1880. 



of a liorse respectively, aud yielded iu the milk and excretions of the cow, and in 

 the excretions of the horse. Here, again, the exigencies of the investigation he 

 undertook were beyond the reach of the kno^\'n methods of the time. Indeed, rude 

 as the art of agriculture is generally considered to be, the scientific elucidation of 

 its practices requires the most refined, and very varied, methods of research ; and 

 a characteristic of the work of Boussingault may be said to be, that he has fre- 

 quently had to devise methods suitable to his piu'pose, before he could grapple with 

 the problems before him. 



In 1839, chiefly in recognition of his important contributions to agricidtural 

 chemistry, Boussingault was elected a member of the Institute ; and in 1878, 

 thirt3'-nine years later, the Council of the Royal Society awarded to him the 

 Copley Medal, the highest honour at their disposal, for his numerous and varied 

 contributions to science, but especially for those relating to agriculture. 



The foregoing brief historical sketch is sufficient to indicate, though but in broad 

 outline, the range of existing knowledge on the subject of agricultural chemistry 

 prior to the appearance of Liebig's memorable work in 1840. It will be seen that 

 some ^ery important and indeed fundamental facts had already been established iu 

 regard to vegetation, and that Boussingault had not only extended inquiry on that 

 subject, but he had brought his own and previous results to bear upon the elucida- 

 tion of long-recognised agricultural practices. There can be no doubt that the data 

 supplied by his researches contributed important elements to the basis of established 

 facts upon which Liebig founded his brilliant generalisations. Accordingly, in 

 1841, Dumas and Boussingault published, jointly, an essay which afterwards 

 appeared in English under the title of ' The Chemical and Physiological Balance of 

 Organic Nature ; ' and, in 1843, Boussingault published a larger work, which 

 embodied the results of many of his own previous original investigations. 



But there can be no doubt that the appearance of Liebig's two works, which 

 were contributions made in answer to a request submitted to him by the committee 

 of this Section of the British Association, constituted a very marked epoch in the 

 history of the progress of agricultural chemistry. In the treatment of his subject 

 he not only called to his aid the previously existing knowledge directly bearing 

 upon it, but he also turned to good account the more recent triumphs of organic 

 chemistry, many of which had been won iu his own laboratory. Further, a marked 

 feature of his expositions was the adoption of what may be called the statistical 

 method — I use the word statistical rather than quantitative, as the latter expression 

 has its own technical meaning among chemists, which is not precisely what I wish 

 to convey. 



It seems that, notwithstanding the conclusive evidence afforded b)' the direct 

 experiments of De Sausaure and his predecessors, vegetable physiologists continued 

 to hold the view that the humus of the soil was the source of the carbon of vege- 

 tation. Not only did Liebig give full weight to the evidence of the experiments of 

 De Saussure and others, and illustrate the possible or probable transformations 

 within the plant by facts already established in organic chemistry, but he demon- 

 strated the utter impossibility of humus supplying the amount of carbon assimilated 

 over a given area. He pointed out that humus itself was the product of previous 

 vegetable growth, and that it could not therefore be an original source of carbon ; 

 and that, from the degree of its insolubility, either in pure water or in water con- 

 taining alkaline or earthy bases, only a small portion of the carbon assimilated by 

 plants could be derived from the amount of humus that could possibly enter the 

 plant in solution. He maintained that, so far as humus was beneficial to vegeta- 

 tion at all, it was only by its oxidation, and a consequent supply of carbonic acid 

 within the soil ; a source which he considered only of importance in the early stages 

 of the life of a plant, and before it had developed and exposed a sufficient amount 

 of green surface to the atmosphere to render it independent of soil supplies of 

 carbonic acid. 



With regard to the hydrogen of plants, at any rate that portion of it contained 

 in their non-nitrogenous products, he maintained that its source must be water ; 

 and that the source of the oxygen was either that contained in carbonic acid or 

 that in water. 



